Objective: Hydronephrosis (HN) and obstruction are closely associated, but upper urinary tract dilatation can occur without significant obstruction. Despite some pitfalls, conventional ultrasonography and diuretic renography (DR) are the main means of evaluation of HN in children. Recent reports have demonstrated color Doppler ultrasonography (CDUS) to reliably identify ureteric jets in the bladder. The aim of this study was to evaluate this method as a diagnostic tool to distinguish obstructive from non-obstructive dilatations of the upper tract.
Methods: We evaluated 51 patients (37 boys and 14 girls), aged 3 months to 14 years (median 4 years), who presented with unilateral grade III and IV hydronephrosis with suspicion of pyeloureteral junction obstruction. All patients underwent DR and evaluation of ureteric jets by transverse CDSG of the bladder within a maximum of 2 weeks. Obstruction was considered in the DR when the hydronephrotic unit showed a differential renal function of less than 40%, or when symptomatic intermittent renal colic was present in older children. The number of ureteric jets was counted over a 5-min period and the frequency calculated for each ureteral orifice. Relative jet frequency (RJF) was defined as frequency of the hydronephrotic side divided by total ureteric jet frequency. Receiver-operating characteristic (ROC) plots were constructed to determine the best cut-off for RJF, in order to identify renal units with obstructive hydronephrosis.
Results: Twenty-three (45.1%) hydronephrotic units were considered obstructed. The mean RJF differed between obstructive (0.09+/-0.15) and non-obstructive hydronephrosis (0.42+/-0.11) (p<0.001). ROC analysis revealed that RJF <0.25 was the best threshold, and correctly discriminated obstruction in 91.2% of the children with a sensitivity of 87% (95% CI 78.6-98.2%) and specificity of 96.4% (95% CI 87.8-99%). The positive likelihood ratio was 24.3 and the area under the ROC curve was 0.92 (95% CI 0.86-0.98).
Conclusions: RJF <25% was found to be a good indicator of obstruction in children with unilateral hydronephrosis. CDUS evaluation of ureteric jets is an easy and non-invasive method that can be used as an initial diagnostic tool, and in follow-up cases, to differentiate obstructed from non-obstructed hydronephrosis in the pediatric population.